The invention relates to an electrolysis device for the purification of acid waters, comprising a cathode, an anode and an ion exchange membrane, the membrane being arranged between the cathode and the anode and held at least continuously in the peripheral area, the upper and lower peripheral areas of the electrolysis device being provided with a large number of feed inlets and discharge outlets connected to the cathode and/or the anode compartment so that a plug flow forms in the cathode and in the anode compartment which, in an ideal version, is characterized by a laminar profile.
The clarification of sulphuric waters from residual open-cast mining sites is presently performed primarily by flooding with extraneous, if necessary, conditioned water owing to the large water volumes required. This process is, however, greatly restricted by the water supplies available, the effort expended for the transfer and the base capacity to be buffered. A clarification of residual open-cast mining sites by liming is, in most cases, inefficient owing to the high stoichiometric excess of basic substances.
DE 19624023 B1 discloses a process for the purification of acid waters in which the water purification process is carried out without admixing any additives to the water to be purified. In contrast to the standard neutralization, the purification effect is not achieved by adding alkaline solution to the water with high pH-value but by separating protons by the electrochemical separation in the cathodic partial reaction of the electrolysis process as shown in the below gross reaction equations:4H++4e−->2H2  (1)4H2O+4e−->2H2+4OH−  (2)
Analogously, the simultaneous electrochemical reduction of the oxygen dissolved in the water to hydroxide ions is generally of neutralizing effect.2H2O+O2+4e−->4OH−  (3)
The reaction (3), however, contributes only little to the cathodic water purification. The use of an ion exchange membrane between the anode and the cathode compartment of the electrolysis cell additionally effects that for raising the pH-value—and for the hydrolysis and precipitation of aluminium and heavy metal ions involved—the salt content of the waters is also considerably reduced. To this end, the cathodic water purification process is coupled with an anodic synthesis process. If there are sulphate ions, the following reactions may take place on the anode side:2H2O->4H++O2+4e−  (4)2SO42−->S2O82−2e−  (5)
In a reaction according to equation (4) the forming protons are saturated by the sulphate ions migrating into the anode compartment, where sulphuric acid is first formed and concentrated. In the second case, sulphate ions are oxidized to give peroxodisulphate and enriched in the anode compartment. In subsequent processes it is possible to recover these products. Similarly, it is also possible to utilize the hydrogen formed in the cathode reaction as a product.
GB 2057507 A or DE 36 14 005 A1 describe electrolysis devices which are generally suited for the before-mentioned processes. Electrolysis cells as known for industrial use in chlor-alkali electrolysis plants are described in DE 196 41 125, DE 197 40 637 or DE 19641 125. Among other components such cells are made up by a cathode and an anode compartment housing the cathode and the anode, resp. The ion exchange membrane is located between the electrodes, and the interior of each compartment is subdivided by the electrode into an electrode chamber and an electrode back chamber. The electrode chamber is bounded by the membrane and the electrode and the electrode back chamber by the electrode and the respective rear cell wall. Each cell has a feed inlet and a discharge outlet.
A disadvantage involved in these theoretically known processes and the known devices is that very high voltages must be applied to the known electrolysis devices in order to purify fluids the ion concentration of which is very low as compared to conventional electrolysis processes, as for example the chlor-alkali electrolysis, and their conductivity therefore very poor.